Battery-powered clock



NOV. 24, 1970 INGENITO ETAL 3,541,778

BATTERY-POWERED CLOCK I 4 Sheets-Sheet 1 INVENTORS MICHAEL J'- ING'ENITO FRANK l/V- STEZL WAGEN Filed April 5.- 1968 NOV. 24,1970 M [NGENITQ ETAL 3,541,778

BATTERY-POWERED CLOCK 4 Sheets-Sheet 2 Filed April 5. 1968 INVENTORS MICHAEL J. IMG fN/TO BY FQANK w. STEIJLWAaEN Z 1 F Hz ,9-

NOV.24, 1970 [NGENITQ ETAL 3,541,778

' BATTERY-POWERED CLOCK Filed April 5, 1968 4 Sheets-Sheet :5

'l a; 6g 55 /I I I BY FRANK wan-11. WAGEN A 7 TOR/V515 I I I l L raw/N6 FORK OSC/LTQQ M. J. INGENITO ET AL BATTERY-POWERED CLOCK Nov. 24, 1970 Filed April 5, 1968 E I55 b 4 Sheets-Sheet 4 iaai INVENTORS M/CWAIEL J INGE'NITO FRANK W1 STELLWAGEN dTi'ORNEYS I I l I I I United States Patent 01 fice BATTERY-POWERED CLOCK Michael Joseph Ingenito, Bronx, N.Y., and Frank W. Stellwagen, Stamford, Conn., assignors to General Time Corporation, Stamford, Conn., a corporation of Dela- Ware Filed Apr. 5, 1968, Ser. No. 719,087 Int. Cl. G04c 13/02 U.S. CI. 5823 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to battery powered clocks and, more particularly, to battery powered clocks driven by means of a synchronous electrical motor.

Since the advent of the transistor and related solid state devices, various electrical battery powered clocks and watches have been developed and commercialized. In one approach, a tuning fork is used as a timing standard and is used to drive the hands of the clock through an escapement mechanism. Tuning forks, however, usually operate at relatively high frequencies, e.g., 300 hertz, and, therefore, the escapement mechanism must be exceedingly accurate if it is to operate on the order of 300 steps per second to produce a one revolution per second rotating speed as would be required for driving a sweep second hand. In another approach, the battery powered transistor circuit is utilized to sustain the oscillatory movement of a pendulum. A reasonable pendulum, however, must be fairly long and, therefore, pendulum movements are feasible only in the larger mantel clocks. Still another approach has been to use the battery powered transistor circuit to sustain motion of a balance wheel mechanism. Balance wheel mechanisms require hairsprings and, as a result, the timekeeping accuracy is impaired and the unit is relatively shock sensitive.

Furthermore, the oscillatory or reciprocating motion of a tuning fork, pendulum, or balance wheel is converted to the necessary rotary motion through an escapement mechanism. Not only are escapement mechanisms undesirable from the mechanical standpoint, but they also place a mechanical load upon the oscillatory timekeeping standard thereby adversely affecting the over-all timekeeping accuracy.

Various battery powered clocks including synchronous motors have been proposed in attempts to overcome the aforementioned shortcomings. See, for example Pat. No. 2,814,769 isseued to Williams, Pat. No. 2,864,018 issued to Aeschmann, Pat. No. 3,121,832 issued to Haskell et al., and Pat No. 3,250,066 issued to Engelhardt et a1. These synchronous motor battery powered clocks have suffered from one or more severe disadvantages which have prevented their commercial exploitation. The proposed clock movements are either prohibitively expensive, or found to have relatively poor timekeeping ability, or require substantial energizing current resulting in undesirably large battery requirements, a short battery life, or both.

An object of this invention is to provide a battery powered clock with a current drain of less than 400 microamperes so that at least a years operating life can 3,541,778 Patented Nov. 24, 1970 2 be obtained from a single commercially available D size dry cell. A further object is to provide such a clock movement which can be produced at competitive prices. Still another object is to provide a battery powered clock which has timekeeping capability. Yet another object is to provide a very compact battery powered clock movement smaller than most of the existing inexpensive clock movements.

The clock movement according to this invention includes a unique synchronous timer motor, discussed in more detail in copending application Ser. -No. 719,125 filed in the name of Frank W. Stellwagen on Apr. 5, 1968, now Pat. No. 3,469,131, having a common assignee with this application. A tuning fork is used as a timekeeping standard for the clock and is incorporated in a tuning fork oscillator circuit. The operating frequency of a motor drive circuit is controlled by the tuning fork oscillator, the motor drive circuit being designed to provide signals to a motor of the type required for an efiicient motor operation. The electronic circuits are designed to minimize power dissipation and to, at the same time, minimize the number of components to reduce costs and space requirements. In order to meet the basic objectives of long operating life with minimum battery requirements, the transistors in the electronic circuits are selected having characteristics properly related to the battery discharge characteristics as will be discussed in more detail hereinafter.

The manner in which the foregoing and other objects are achieved according to the invention is described more fully in the following specification which sets forth an illustrative embodiment. The drawings are part of the specification wherein:

FIG. 1 is a perspective view illustrating the motor with the housing and rotor bearings removed;

FIG. 2 is a plan view of the rotor and the surrounding portion of the stator structure;

FIGS. 3A and 3B illustrate, respectively, the magnetic paths for the AC energizing flux and the DC permanent magnet flux;

FIG. 4 is an enlarged diagram illustrating the relationship between the fluxes passing through the rotor teeth and the adjacent pole faces of the stator;

FIG. 5 is a plan view of a completed clock assembly including the timer motor, gear train, tuning fork oscillator and motor drive circuit;

FIG. 6 is a stretch-out diagram arranged to more clearly illustrate the gear train coupled to the timer motor;

FIG. 7 is a partial perspective illustration of the starter and time setting assembly for the clock shown in FIGS. 5 and 6;

FIG. 8 is a perspective view illustrating the tuning fork and associated pickup and drive coils as included in the clock shown in FIG. 5;

FIG. 9 is a schematic illustration of the tuning fork oscillator and motor drive circuit which is coupled to the timer motor in the clock assembly illustrated in FIG. 5;

FIG. 10 is a diagram illustrating the relationship of the transistor saturation voltages to the operating life of a battery powered clock; and

FIG. 11 illustrates the wave shapes produced by the tuning fork oscillator and motor drive circuits in FIG. 9.

The synchronous timer motor described in the illustrative embodiment is designed to operate on a hertz supply and rotate at 600 rpm. (10 rotations per second). The rotor for this motor includes a permanent magnet 10 sandwiched between a pair of notched rotating discs 11 and 12, this assembly being arranged to provide a magnetized rotating circuit for the rotor. Each rotor disc is notched to provide 15 equally-spaced teeth to thereby form a 30-pole motor. The teeth are staggered so that when the rotor is viewed along the axis, as shown in FIG. 2, the teeth 16 on one of the discs appear located between adjacent teeth 17 of the other disc.

Permanent magnet and discs 11 and 12 are aligned on an arbor 20 between suitable bushings 18 and 19 and secured by an epoxy bond. Epoxy available under the trade name Bond Master M-645 (30 parts hardener to 100 parts resin) cured under pressure at a temperature of 300 F. has been found to provide satisfactory results.

The permanent magnet is preferablya barium ferrite material such as is available under the trade name Leyman IH Plastiform, which is relatively inexpensive in the sizes required for the rotor. The diameter of the permanent magnet is approximately the same as the diameter at the base of the rotor teeth. Permanent magnet 10 is magnetized after the rotor is assembled so that rotor disc 11 becomes a north pole and the disc 12 becomes a south pole. The magnetizing energy is controlled so that the open circuit leakage between discs 11 and 12 is approximately 100 gauss.

The stator for the motor includes a generally rectangular laminated core configuration having a leg 30 which passes through the center of an energizing winding 31 as well as pole pieces 32 which pass outside the coil and surround a generally circular opening which accommodates the rotor.

The energizing winding is concentrically wound about a rectangular nylon bobbin 33. Preferably, the winding is center tapped as can be achieved inexpensively through a bifilar winding technique. The length of the completed winding is approximately five times the radius of the winding in order to provide the lowest cost and copper loss. The winding is formed using 39 gage wire and includes 4,500 turns to provide an 880 ohm winding.

The cross-section of leg 30 of the stator core as it passes through the energizing winding has a square configuration as this provides a more efficient coupling relative to the winding. However, in other areas, the stator core need be no thicker than the thickness of the rotor plus a proper allowance for leakage flux. Therefore, to minimize the use of iron in the stator core to thereby reduce costs, the thickness of the stator in all areas other than leg 30 is determined by the leakage flux at a given section and the thickness of the rotor which is approxi-- mately .090 inch. Laminations 34 are added to the portion of the stator core passing through the energizing winding to build up the stator core thickness to a square crosssection which is .15 6 inch on a side.

As can be seen in FIG. 1, there is relatively little space between the winding and the stator core as the latter passes around the outside of the winding. By so constructing the stator, the length of the stator magnetic path is minimized thereby reducing iron losses, and the quantity of iron required for construction of the stator is minimized thereby reducing costs.

The portion of the stator core passing outside the energizing coil 31 is separated to provide a permanent air gap in the magnetic circuit between pole pieces 32. This permanent air gap includes the generally circular opening which accommodates the rotor. The periphery of the opening is notched to provide stator pole faces 40 on one side of the opening and stator pole faces 41 on the other side, the angular displacement between adjacent pole face centers being 24 corresponding to the displacement of the teeth on each of the rotor discs. As can be seen in FIGS. 1 and 2, there are seven stator pole faces on each side of the rotor. The stator pole faces 40 are placed symmetrically relative to the pole faces 41 so that if the teeth of the north polerotor disc 11 are centered on pole faces 40 on one side of the rotor, the teeth of the south pole rotor disc 12 will be centered on stator pole faces 41 on the other side of the rotor.

When the motor is in operation there are two flux paths, one for the AC energizing coil flux, which is shown schematically in FIG. 3A, and the other for the DC permanent magnet flux, which is shown in FIG. 3B.

The AC flux is generated by energizing coil 31 and passes through the stator to the stator pole faces, across the air gap, through rotor discs 11 and 12, back across the air gap into the stator to complete the magnetic circuit back to the energizing coil. Significantly, although the rotor includes a permanent magnet, the AC energizing flux does not pass through the permanent magnet. Permanent magnets normally have a high reluctance and therefore substantial iron losses would result if it were necessary for the energizing flux to pass through the permanent magnet. As shown in FIG. 3A, the energizing flux passes through rotor discs 11 and 12 and thereby bypasses the permanent magnet.

I The DC flux path is shown in FIG. 3B and goes from the north pole of permanent magnet 10, through the teeth of rotor disc 11, across the air gap and through the stator pole faces, back across the air gap and through the rotor disc 12 to the south pole of permanent magnet 10. As shown in FIG. 2, the teeth of discs 11 and 12 are staggered, but are always sufliciently close to a pole face to complete a DC magnetic path. When the motor is rotating synchronously, the teeth are aligned with stator pole faces generally as shown in FIG. 2 when the AC energizing flux is maximum thereby providing maximum coupling between the teeth of discs 11 and 12 through an adjacent stator pole face at the instant of maximum torque generation. 7

The AC and DC magnetic fluxes combine to provide a substantially greater torque than could be achieved by either hysteresis or reluctance type motors. Since the motor torque is approximately proportional to the square of the flux density in the air gap, the additive effect is quite significant.

Consider first the fluxes during a half cycle when the AC fiux (4 is in the direction shown in FIG. 4. In teeth 16 of the north pole rotor disc, the AC flux 5 and the DC flux are additive and represented:

whereas in the teeth 17, the DC flux (qa is in the opposite direction and, therefore, the fluxes oppose one another which can be represented:

Since torque is approximately proportional to the square of the flux density, the combined torque T of a pair of rotor teeth 16, 17, is represented:

During the next half cycle of the AC flux, (qb changes direction and, therefore, the torque T during this half cycle is represented:

Thus, the motor torque is approximately proportional to four times the product of the permanent magnet flux and the energizing flux. From this relationship, it should be noted that the torque increases in direct proportion to increases in the permanent magnetic flux. However, the saturation characteristics in the most confined portions of the magnetic paths (the rotor teeth and stator pole faces) limit the amount of torque multiplication which can be achieved by increasing the strength of the permanent magnet. It has been found desirable to design the motor to operate in a range not normally exceeding 50% of the perm1ssib1e saturation flux density when the permanent magnet flux and peak AC energizing flux are combined. In the motor according to the invention, the permanent flux is approximately ten times as great as the peak energizing flux which, according to Equations 4 and 6 provide a motor torque approximately 40 times greater than could be achieved without the polarized magnetic rotating circuit.

, The magnetic material for the stator circuit and the rotor discs 11 and 12 must be carefully selected.

The magnetic material must have a high permeability which, for the purposes of this specification, can be defined as being in excess of 20,000. High permeability magnetic materials are essential in order to keep the reluctance loss below 5% of the input power.

The magnetic material must also have a high saturation flux density so that a significant torque multiplication can be achieved through the use of the permanent magnet flux without requiring an abnormally large structure. For the purposes of this specification, high saturation flux densities are defined as saturation densities exceeding 10,000 gauss.

It is further essential that the magnetic material have a relatively small hysteresis loop so that the hysteresis losses at the motor operating frequency are maintained within bounds. For the purposes of this specification, a low hysteresis material can be defined as one in which the hysteresis loss is below 500 ergs/cc./cycle. Preferably, the magnetic material has a hysteresis loss below 300 ergs/cc./cycle.

An iron alloy magnetic material consisting of at least a 40% nickel content (by weight) has been found to provide a desired combination of high permeability and high saturation flux density as well as a low hysteresis loss. Preferably, the nickel content is maintained between 47- 50%. Such materials have a permeability of approximately 50,000, a saturation flux density of 16,000 gauss and a hysteresis loss of approximately 500 ergs/cc./cyc1e.

In an efficient dry cell powered synchronous motor, the eddy current losses must also be reduced to a minimum. To achieve this, the magnetic material is selected having a relatively high electrical resistivity which, for the purposes of this application, can be defined as a resistivity greater than 60 microhm-cm. Preferably, the resisitivity is within the range of 75-90 microhm-cm. High resistivity is achieved in the magnetic material through the addition of silicon or molybdenum but the addition of silicon or molybdenum has been found to adversely affect the magnetic materials permeability and saturation flux density, while, on the other hand, having the desirable effect of reducing the hysteresis losses. Approximately 3% (by weight) of either molybdenum or silicon is found to increase the resistivity into the preferable range without precluding the high permeability for high saturation flux density characteristics of the material. The addition of approximately 3% silicon or molybdenum also has been found to reduce the hysteresis losses into the desirable range of below 300 ergs/ cc./ cycle.

Relatively thin laminations are utilized to further reduce eddy current losses. Iron-nickel alloy materials with a thickness of approximately six one-thousandths of an inch (0.006) can be produced at moderate cost and, hence, laminations of this thickness were selected for the motor in the illustrative embodiment.

The selection of relatively thin laminations on the order of six one-thousandths of an inch is significant for another reason. In the design of a motor, it is desirable to minimize the air gap. However, small air gap tolerances are usually achieved by resorting to more expensive machining andconstruction techniques, which are generally quite costly. For inexpensive timer motors, the rotor and stator laminations are preferably produced using stamping techniques. With thin laminations on the order of six one-thousandths of an inch, the stator and rotor laminations can be punched at moderate cost using high-speed 6 progressive carbide dies while maintaining the maximum air gap within five one-thousandths of an inch (0.005). This is achieved in specifying suitable plus tolerances for the rotor discs and minus tolerances for the stator bore so that as the dies wear the air gap will be reduced and therefore the air gap never exceeds five-thousandths of an inch. Thus, by using very thin laminations not only are the eddy current losses reduced, but a small air gap can be achieved at moderate cost.

The laminations of the stator core on one side of the rotor are the same as those on the other side and, hence, can be made from the same stampings. Preferably, however, the lengths of the portions passing through the energizing coil are varied in length to provide a lap joint rather than a butt joint. The lap joint reduces reluctance of the magnetic path.

Considerable care must be taken to minimize stray power losses which arise when the flux density ('B) becomes too high. The hysteresis loss is proportional to (B and copper losses are generally proportional to (B An undesirable high flux density (B) can occur if the permanent magnet flux is too high, or the size of the rotor teeth and stator pole faces too small. The wave shape of the motor energizing signal is also very significant. A sine wave source is preferable and a square wave source quite acceptable. However, wave forms having periodic spikes, such as those caused by switching transients, are very undesirable since they create disproportionately high stray losses.

The following data has been obtained for a motor constructed according to the invention with a inch nominal rotor diameter, an air gap not exceeding five-thousandths of an inch, magnetic laminations six-thousandths of an inch and the magnetic material being an iron alloy including 47% (by weight) nickel and 3% (by weight) molybdenum. This magnetic material is found to have a permeability of 30,000, a resistivity of microhm-cm., a saturation flux density of 11,000 gauss and a hysteresis loss of 250 ergs/cc./cycle.

When energized from a 150' hertz sine wave source, the following characteristics were measured:

was, Wont; I, mleromieromicro- Efliciency, amps watts watts percent When the same motor was operated from a 150 hertz square wave source, the following characteristics were measured:

The complete battery powered electric clock including the motor 1 is illustrated in FIG. 5 and in a stretch-out diagram in FIG. 6. In FIG. 6, the various gears and shafts are displaced from their normal positions as shown in FIG. 5 and are placed side-by-side to provide a simpler illustration of the basic gear train.

The motor 1 and associated gear train 2 are mounted between parallel plates 50 and 51 which are maintained in the desired spaced relationship by suitable connecting bolts and spacers between the plates. The stator structure of the motor is secured to the front plate 50 and maintained in position by suitable bolts passing through the laminations of the stator and suitable spacers located between the front plate and the stator. The bolts 35 (FIG. 6), as well as additional bolts passing through holes 36 (FIG. 1), can be used for this purpose.

Arbor 20 which carried the rotor of the motor is journaled between a pair of screw-set bearings '53 and 54 mounted in plates 50 and 51, respectively. The screw settings for these bearings are adjusted to properly center the rotor with respect to the stator after the latter is secured to the front plate. Also, the screw-set bearings are adjusted to provide the proper bearing engagement with the arbor. A flywheel 55 is secured to the arbor between the rotor and rear plate 51, and a pinion 56 is mounted on the arbor near front plate 50.

Pinion 56 drives a large (80 tooth) gear 60 mounted on a shaft 61 journaled between screw-set bearings 62 and 63. A pinion 64 on shaft 61 engages a gear 65 mounted on a shaft 66 journaled on the rear plate 51, and the pinion 67 on shaft 66 engages a gear 68 which is secured to the sweep second hand of the clock through a shaft 69. Gear 68 is secured to a pinion 70 which engages a gear 71 (shown separated at the far left of FIG. 6 for clarity of illustration) mounted on a shaft 72, and pinion 73 associated with gear 71 engages a gear 74. Gear 74 is coupled to a hollow shaft 75 via a friction clutch 76 and the hollow shaft in turn is adapted for coupling to the minute hand of the clock. A pinion 77 is mounted on a hollow shaft 75 and engages a gear 78 mounted on a shaft 79 and the associated pinion 80 drives a gear 81 secured to hollow shaft 82, this hollow shaft being adapted for coupling to the hour hand of the clock.

The gear ratios in the gear train coupling the hands of the clock to the motor are as follows:

A double flanged bushing 83 is mounted in front plate 50 and hollow shafts 82 and 75 coupled to the hour and minute hands, respectively, are concentrically journaled within the bushing. The hub for pinion 77 which supports friction clutch 76 is secured inside the end of hollow shaft 75, and shaft 6 9 coupled to the sweep second hand is journaled through the center of pinion 77.

The starter and time setting mechanism 3 is partially shown in FIGS. and 6, and is illustrated in a partial perspective view in FIG. 7. A knob 90 used for setting the hour and minute hands of the clock is secured to the end of a shaft 91 which passes through the front and rear plates 51 and 50 as shown in FIG. 6. A pinion 94 is chamfered to provide a conical cam surface on one side, and is mounted near the end of shaft 91 at the opposite end from knob 90. A compression spring 92 is positioned surrounding shaft 91 between rear plate 51 and the flanges of a bushing 93 to urge the flat surfaces of pinion 94 toward front plate 50.

When knob 90 is pulled out, shaft 91 moves in the direction of the arrow (FIG. 7) so that pinion 94 engages gear 78. Gear 78 is coupled to the minute hand and, hence, rotation of the knob, when pulled out, sets the minute and hour hands of the clock. This rotational movement is not transmitted back to the second hand of the clock or the motor because of friction clutch 76. The chamfer on opinion 94 provides easy engagement with gear 78 as the knob is pulled out.

The chamfer surface of pinion 94 also serves as a cam surface for the motor starting mechanism. A cam follower 95 is mounted for rotation about a shaft 96 and is secured to an extending arm 97. Ann 97 in turn engages a starter spring 98 which extends from rear plate 51 (FIG. 5). Spring 98 is positioned so that it rests against arm 97 and, so that, in its normal position, the spring clears gear 60, this gear being coupled to the rotor of the motor via pinion 56.

When knob is pulled out to set the clock, the corresponding movement of shaft 91 causes the cam surface to engage cam follower to thereby rotate arm 97 about shaft 96. As arm 97 rotates, spring 98 is tensioned and moved into engagement with the teeth of gear-60. Subsequently, when knob 90' is released, shaft 91 snaps back into the original position thereby releasing the cam follower, arm 97 and spring '98. As spring 98 returns to its normal position, rotational movement is imparted to gear 60 which in turn is transferred to the rotor of motor 1 through pinion 56. The spring is designed so that the rotational speed imparted to the rotor is slightly greater than the synchronous speed of the motor. Therefore, as the rotor begins to slow down, it drops into synchronous rotation. Flywheel 55 adds inertia to the rotor to decrease the rate at which the rotor speed decreases to thereby significantly improve the chances of the rotor locking into synchronous rotation.

Thus, it should be noted that when the user of the clock sets the hands, he automatically starts the clock motor. As a result, the starting of the motor takes place automatically and the user is not aware that the motor is being hand started. In a battery powered clock, the manually started motor according to this invention is preferable to motors of the self-starting variety because in the latter electrical energy is unnecessarily expended during the starting interval and the self-starting characteristic has a tendency of wasting electrical energy during normal operation.

In the illustrative embodiment, the motor is powered from a primary cell (dry cell) 100 shown schematically in FIG. 9. This primary cell can be of a conventional D size with an open circuit potential of 1.55 volts. Tuning fork oscillator 101 provides the frequency standard, and a motor drive circuit 102 operates at a frequency controlled by the oscillator to energize the motor coils.

A tuning fork 103 is mounted between plates 50 and 51 of the clock housing in any convenient fashion and the pickup and drive coils 104 and 105, respectively, are suitably mounted between the tines of the tuning fork. The pickup coil is wound around a cylindrical permanent magnet core 106 and includes 8,000 turns of No. 48 wire to provide a coil resistance of approximately 1,500 ohms. The drive coil is wound concentrically around the pickup coil and includes 4,500 turns of No. 46 wire to provide a coil which also has a resistance of approximately 1,500 ohms. The thickness of the coil structure is slightly less than the distance between the tines of the tuning fork to provide just enough clearance for free vibration of the tuning fork. Preferably, the pickup coil is located inside the drive coil to provide better pickup signal sensitivity. The coils are wound concentrically and located between the tines of the tuning fork to provide a more compact structure than would otherwise exist if the coils were located outside the tuning fork.

Tuning fork 103 is of conventional design and is constructed to oscillate at 300' hertz. Tuning forks oscillating at lower frequencies could be used but are less desirable because of their larger size and orientation sensitivity. A disc permanent magnet 107 is magnetized axially and mounted on an internally threaded hub 108 which cooperates with a stationary stud 109 secured to the clock housing. The position of this permanent magnet closely adjacent one of the tines of the tuning fork has an eifect upon the tuning fork oscillating frequency. Therefore, if the permanent magnet disc 107 is rotated, it moves transversely of the tuning fork tine and, therefore, the effect of the permanent magnet upon the tuning fork frequency can be varied as desired. In this fashion, minor adjustments in the tuning fork frequency can be achieved.

The tuning fork oscillator 101 includes a transistor Q which is of the NPN type. The emitter of the transistor is connected to the negative terminal of battery 100, and the collector thereof is connected to the positive terminal Transistor Q 2N292S Capacitor 110-.1 mfd. Capacitor 111.1 mfd. Resistor 112330K Capacitor 110 reduces the magnitude of any high frequency oscillation so that spurious high frequency oscillations cannot trigger transistor Q into a conductive state. Capacitors 110 and 111 also serve to shift the electrical resonant frequency of the oscillator into the vicinity of the natural resonant frequency of the tuning fork.

Capacitor 11 provides DC isolation between the positive battery terminal and the base of transistor Q since otherwise the battery potential would be applied to the base through'the relatively low impedance of coil 104. Resistor 112 has a much higher impedance than coil 104 and provides a slight positive bias tending to render the transistor slightly conductive so that the'oscillator will be self-starting. Resistor 112 must be sufficiently large to avoid unnecessary power loss during normal operation.

When the tuning fork oscillator is initially energized, a small current flows through coil 105, resistor 112 and the base-emitter'circuit of transistor Q to initially render the transistor slightly conductive. As a result, the collectoremitter circuit permits a larger current flow through drive coil 105 which in turn imparts motion to the tines of the associated tuning fork 103. Movement of the tines modulates the reluctance of the flux path for permanent magnet 106, and the resulting change in flux induces a signal in pickup coil 104 which is of the proper polarity to increase conduction of the transistor. The coupling is regenerative and, therefore, additional current flows through the drive coil. The transistor is quickly driven into saturation.

When the lines of the tuning fork reach the end of their stroke and reverse direction, the polarity of the signal induced in the pickup coil reverses and, when applied to the base of transistor Q tends to, render the transistor nonconductive. This signal developed in the pickup coil mustovercomethe bias provided by. capacitr111 and, hence, the nonconductive interval 130, as shown in FIG. 11(a) is shorter than the conduction interval. Subsequently, when the tines again reverse. direction the transistor becomes conductive and the cycle repeats.

v As can be seen in FIG. 11(a), which shows the signal on the collector of transistor Q there is a fairly large switching transient 131 which is caused mainly by the considerable inductance of drive coil 105. As was previously mentioned, switching transientsadversely affectthe operation of the motor and therefore the wave shape in FIG. 11(a) is not suitable for application to the motor.

Motor drive circuit 102 is a bistable circuit which produces square Wave suitable for application to motor 1. The separate motor drive circuit avoids loading of the oscillator circuit and also provides a frequency reduction which permits use ofa higher tuning fork frequency than would otherwise be possible. The drive circuit includes transistors Q and Q which are both of the NPN type. The emitters of the transistors are connected to the negative terminal of battery 100, and the collectors thereof are connected to the positive terminal via coils 113 and 114, respectively, which are the two coils of the center tapped energizing winding 31 of the motor. The transistors are cross coupled by resistor 115 connected between the collector of transistor Q and the base of transistor Q and by resistor 116 connected between the collector of transistor Q and the base of transistor Q The anodes of coupling diodes 117 and 118 are connected to the bases of transistors Q and Q respectively, and their common cathode connection is connected to the negative battery terminal via a resistor 119. The common cathode connection is also coupled to the collector of transistor Q in the tuning fork oscillator circuit via a coupling capacitor 120.

The values of components in the drive circuit are as follows:

Transistors Q and Q 2N2925 Resistors and 11633K Resistor 119-330K Capacitor 120-.1 mfd.

Assume initially that transistor Q is conductive. Current flows through coil 113 and the collector-emitter circuit of transistor Q thereby energizing the winding with a pulse 133 as indicated in FIG. 11(b). The collector of transistor Q is at a potential close to that of the negative battery terminal and therefore transistor Q is biased to cut-off via resistor 115. Since transistor Q, is nonconductive, its collector is positive and maintains transistor Q conductive via resistor 116.

When a negative pulse (FIG. 11(a)) appears at the collector of transistor Q it is coupled to the bases of transistors Q and Q via capacitor 120 and diodes 117 and 118. The negative pulse affects transistor Q then in the conductive state and drives the transistor into cutoff. As a result, the collector of transistor Q becomes positive and, through resistor 115, renders transistor Q conductive. The collector of transistor Q goes negative and transistor Q is therefore maintained in a nonconductive state. The negative pulse therefore changes the cOnductive states of the transistors and a pulse 133 is supplied to Winding 114 as indicated in FIG. 11(c).

Each time a negative pulse is applied to the motor drive circuit, the transistors change state and, hence, the circuit operates in on-off fashion. Since the negative pulse 130 occurs at a 300 hertz rate, the windings 113 and 114 are energized at a hertz rate.

The circuits shown in FIG. 9 are relatively simple and comprise a rather modest number of components in view .of the functions performed by the circuits. In the drive circuit, it should be noted that the coupling capacitors that normally bypass the coupling resistors 115 and 116 have been eliminated. It has been found that the inductance of coils 113 and 114 assists in the switching functions and eliminates the need for these capacitors.

As is illustrated in FIG. 5, rear plate 51 can be a nonconductive substrate with the electrical components such as 121 mounted on one side and interconnected with printed circuits on the other. This arrangement provides a cost-saving and a size reduction.

It is essential that transistors Q Q and Q have loW saturation voltages in battery powered clocks. A high saturation voltage increases the power dissipation of the transistors, but this effect does not normally adversely affect the life of the battery in the clock by more than 10%. Of greater significance is the relationship illustrated in FIG. 10.

When a new dry cell is inserted, the terminal voltage will be approximately 1.55 volts and in time will decrease along a curve 140. The circuit in FIG. 9 wherein the transistors are selected having a saturation voltage of less than 0.2 volt, the circuit is found to operate reliably until the battery voltage drops to approximately 1.0 volt. Thus, dotted line 143 indicates the cut-off voltage and line 141 indicates the life of the unit which in this case is approximately 12 months.

If the saturation voltage of the transistors increases by 0.2 volt to, for example, 0.4 volt, dotted line 144 would represent the cut-off point at 1.2 volts which would occur after approximately seven months instead of twelve. If the saturation voltage increased to .6 volt, the life would be reduced to about four months. Accordingly, the transistor emitter-collector saturation voltage must be kept below 0.2 volt if a reasonable long battery life is to be achieved.

In the clock, including the unique motor according to the invention, the applied current drain is divided approximately as follows:

Microamps Tuning fork oscillator 75 Motor and motor drive circuit 325 Total 400 With this current drain and reliable operation down to a battery terminal potential of 1.0 volt, operation for more than twelve months can be achieved on a single D size dry cell.

The motor pull-out torque under these conditions is found to be better than 120 gr.-mm., which is more than twice the torque normally required for the clock alone, and hence, the unit can be used to also perform auxiliary functions.

The battery powered clock according to the invention is also quite compact. The entire clock can be housed in an enclosure a little more than three inches square and one inch deep.

While only one illustrative embodiment has been described in detail, it should be obvious that there are numerous variations within the scope of the invention. The invention is more specifically defined in the appended claims.

What is claimed is:

f1. In a battery powered electric clock, the combination primary cell means for energizing the clock;

a controlled frequency oscillator energized by said primary cell means and operative to produce a timing signal at a predetermined frequency, said oscillator including,

a tuning fork a first solid state device,

a pickup circuit for sensing the mechanical oscillation of said tuning fork, and coupled to said solid state device for applying a corresponding electrical signal to effect the conductive state thereof, said pickup circuit including,

a permanent magnet producing flux passing through at least one of the tines of said tuning fork,

a pickup coil operative to sense a change in flux of said permanent magnet in response to oscillation of said tuning fork and to generate a corresponding electrical signal, and

capacitor means coupled across said pickup coil,

a drive coil coupled to said tuning fork to impart motion thereto when energized, said drive coil being connected to said first solid state device and energized according to the conductive state thereof;

an efficient synchronous motor including a winding;

and

a motor drive circuit energized by said primary cell and including,

a second solid state device connected to said Winding to energize the same when conductive, the potential drop across said second solid state device when fully conductive being less than 0.2 volt, and

circuit means coupling said second solid state device to said controlled frequency oscillator to cause operation of said second solid state device in on-off fashion at a rate determined by said predetermined frequency of said tuning signal.

2. A battery powered clock according to claim 1 wherem said first solid state device is a transistor and further including means for normally biasing said transistor into a slightly conductive state.

3. A battery powered clock according to claim 2 wherein said transistor has a collector-emitter saturation potential of less than 0.2 volt.

4. The battery powered clock according to claim 1 wherein said pickup circuit comprises a pickup coil and wherein said pickup coil and said drive coil are located between the tines of said tuning fork to provide a compact structure.

5. In a battery powered clock, the combination of:

a mechanical resonating device,

an electrical oscillator including said mechanical resonating device, said oscillator being operative to produce a timing signal at a frequency determined by said resonating device;

a synchronous motor including a polarized rotating magnetic circuit including a spaced apart pair of magnetic rotor discs with a permanent magnet therebetween,

an energizing winding, and

a stator core passing through said winding for distributing magnetic flux created by said energizing winding to a plurality of stator pole faces surrounding said rotating magnetic circuit; and

a motor drive circuit including at least one solid state device connected to energize said energizing winding when conductive, and

circuit means including a coupling diode so coupling said solid state device to said oscillator that said solid state device operates in on-off fashion at a rate determined by said timing signal.

6. The battery powered clock according to claim 5 wherein said energizing winding includes two coils and said solid state device in connected to one of said coils to energize the same, and wherein said motor drive circuit further comprises a second solid state device connected to energize the other of said coils, said solid state devices being interconnected to become conductive alternately.

7. The battery powered clock according to claim 6 wherein said solid state devices are transistors.

8. The battery powered clock according to claim 7 wherein said transistors have a collector-emitter saturation voltage of less than 0.2 volt.

9 The battery powered clock according to claim 5 wherein said mechanical resonating device is a tuning fork.

10. The battery powered clock according to claim 9 wherein said electrical oscillator includes a pickup circuit for sensing the motion of said tuning fork and for providing a corresponding electrical signal,

a transistor responsive to said signal and operative in a substantially on-off fashion, and

a drive coil connected to said transistor and operative to excite said tuning fork when energized.

11. In a battery powered electric clock, the combination of primary cell means for energizing the clock;

a controlled frequency oscillator energized by said primary cell means and operative to produce a timing signal at a predetermined frequency, said oscillator including,

a tuning fork,

a first solid state device,

a pickup circuit for sensing the mechanical oscillation of said tuning fork, and coupled to said solid state device for applying a corresponding electrical signal to effect the conductive state thereof,

a drive coil coupled to said tuning fork to impart motion thereto when energized, said drive coil being connected to said first solid state device and energized according to the conductive state thereof;

an efficient synchronous motor including a two coil winding; and a motor drive circuit energized by said primary cell and including,

first and second transistors connected to the coils of said winding to energize the respective coil when conductive, the potential drop across said transistors when fully conductive being less than 0.2 volt, said first and second transistors being interconnected to energize their respective coils alternately, and coupling diodes for coupling said first and second transistors to said controlled frequency oscillator to cause operation of said transistors in onoif fashion at a rate determined by said predetermined frequency of said tuning signal.

References Cited UNITED STATES PATENTS 1,560,056 11/1925 Horton 84-409 X 3,250,066 5/1966 Engclhardt et a1. 58-23 3,421,309 1/1969 Bennett 58-23 RICHARD B. WILKINSON, Primary Examiner E. C. SIMMONS, Assistant Examiner US. Cl. X.R. 31046 

